Next-generation WiFi standard (802.11 n) promises up to 600 Megabits per second (Mbps) in wireless transmission data rate. Such a wireless transmission data rate is very interesting, as it renders possible “true” wireless applications. At this data rate, triple-play services (data, voice, and video) can be supported in an enterprise or a home environment. The standard calls for MIMO (Multiple-Input-Multiple-Output) implementation, which entails having more than one antenna at the access points. By transmitting data on two or more different antennas, the data rate can be increased without having to increase transmission power and/or bandwidth.
Most current 802.11 n systems utilize antennas that are omni directional, i.e. where the signal is transmitted in all directions. Use of omni directional antennas presents mainly two disadvantages: short transmission distance and interference. Both of these problems contribute to lower the data rate while also rendering the wireless connection unreliable. These problems were not addressed in previous versions of the WiFi standard (802.11 a/b/g). However, with the promise of WiFi replacing Gigabit-Ethernet, these problems have to be addressed to make next-generation WiFi deliver on its promise of 600 Mbps wireless transmission data rate.
In U.S. patent application Ser. No. 11/947,759 “Dynamic radiation pattern antenna system”, Frigon et al. propose to utilize a directional antenna that focuses the signal towards a mobile terminal as a receiver, alleviating the problems of short transmit distance and interference simultaneously. The directional antenna is coupled with a “smart” algorithm called DRPD (Dynamic Radiation Pattern Diversity) which is able to intelligently steer the beam in a particular direction in order to provide the mobile terminal with a reliable connection. As well, the DRPD entails converging towards a more “dynamic” approach to antennas rather than the current “static” approach typically found in most commercial products. Coupled with MIMO, DRPD provides the mobile terminal with the highest possible data rate in any given environment (office or home).
For doing so, Frigon et al. use a novel and breakthrough leaky-wave antenna (LWA) which is a first of its kind. This antenna is shown in FIG. 1. It is based on metamaterial composite right/left-handed (CRLH) technology developed by Dr. Christophe Caloz. The backfire-to-endfire CRLH LWA provides for the first time the capability of scanning the entire free space with high directivity and flexibility, without requiring any cumbersome and power-hungry (lossy) feeding network compared with conventional antenna arrays. This LWA is fundamentally a traveling wave (as opposed to resonant) antenna, where backward/broadside/forward radiation is obtained when the structure is tuned to propagate a backward/“standing”/forward wave. FIG. 1(a) illustrates the CRLH LWA, while FIG. 1(b) depicts a varactor-based CRLH LWA.
By incorporating varactor diodes (i.e. capacitors with a capacitance varying as a function of their reverse-bias voltage) in the structure, the beam can be scanned in real-time. It is then possible, by electronically tuning the varactor diodes' reverse-bias voltages, to achieve full-space scanning at a fixed operation frequency. Typical simulated and measured radiation patterns of a CRLH LW antenna are shown in FIG. 2. By electronically changing the bias-voltages of the CRLH LW antenna, a wide and continuous range of radiation patterns for a single antenna element can be efficiently achieved.
Power angular spectrum (PAS) parameters are used to define an antenna's radiation pattern. PAS parameters comprise angle of arrival, angular spread and power gain. The PAS parameters are dominated by large scale effects and vary in an order of several tens of seconds. It is thus possible to adapt the radiation patterns to long term statistics of these parameters instead of their instantaneous values. Using simulations, it has been shown that such approach results in penalties in the order of 1.5 dB when such a long term approach is used. This long term approach proves interesting only if PAS parameters can be accurately estimated.
However, with current systems and methods, it is not possible to set an antenna's optimal radiation pattern of a DRPD without sufficient information on the required radiation pattern. There is thus a need for a radiation pattern control system for accurately acquiring information about a signal and setting a corresponding radiation pattern.